Look at the topographic map for illustration. Hiking and climbing routes are marked according type (glacier, rock, walls...)
There are two English language guidebooks that cover Galdhopiggen:
A. Dyer et al's guidebook "Walks and Scrambles in Norway" ISBN 978-1904466253.
Bernhard Pollmann's "Norway South" also covers it, but is out-of-print and is more difficult to find (ISBN 978-3763348077).